RELATIVITY

Einstein realized that the speed of light is always the
same. He then calculated that an object travelling near this speed acts
strangely: it shrinks in length, increases in mass, and time slows down. He
also calculated that mass alters space. So small objects do not travel in
straight lines near a large object – instead they follow the distortions
in space made by it. Centuries after gravity was identified as a force,
Einstein’s theory of relativity explained why it works the way it
does.

In traditional physics, gravity attracts one mass to another. This
explains why a comet follows a curved path around the Sun. Einstein’s
general theory of relativity explains gravity differently. Masses warp space
and time a bit like heavy balls resting on a sheet of rubber. The bigger the
mass, the more distortion, and the greater the pull of gravity. In 1921
Einstein was proved correct when the light from a star was shown to be bent by
the warping effect of the Sun’s mass.

ACCURATE TIMEKEEPING

The effects of relativity are only detectable when things travel at
very high speeds. To detect them, scientists need accurate clocks that use
atoms to tell the time. Atoms of the element caesium vibrate at a precise rate.
Atomic clocks measure time by counting these vibrations. Clocks such as the one
above use a radio link to a central atomic clock to relay the precise time.

BIOGRAPHY: ALBERT EINSTEIN German, 1879–1955

When Albert Einstein was expelled from school, no one imagined he
would become one of the most brilliant physicists of the 20th century. His
theory of relativity was so strange that people refused to believe it at first.
It was widely accepted only after he won the Nobel Prize for Physics in
1921.